Heretofore, a bilirubin oxidase produced by culturing a microorganism belonging to the genus Aqaricus is known, whose properties have not been clarified (Japanese Published Unexamined Patent Application No. 151193/79). Also, it is reported that a bilirubin oxidase is produced by culturing a microorganism belonging to the genus Myrothecium [N. Tanaka and S. Murao, Agric. Biol. Chem., 46, 2499-2503 (1982)]. This known enzyme shows specific activities on hydroquinone and catechol in addition to bilirubin and biliverdin. As a result of various studies of bilirubin oxidase, it has been found that a wide range of microorganisms of Basidiomycetes produce a novel bilirubin oxidase.